The CAS Registry Mumber 78351-31-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,3,5 and 1 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 78351-31: (7*7)+(6*8)+(5*3)+(4*5)+(3*1)+(2*3)+(1*1)=142 142 % 10 = 2 So 78351-31-2 is a valid CAS Registry Number.